Patent GB-1274581-A (GB)
Title: Improvements relating to methods and apparatus for cutting gears and like toothed members
IPC: B24B53/07
Filed: 1970-01-09
Abstract: 1,274,581. Grinding; trueing grinding wheels. GLEASON WORKS. 9 Jan., 1970 [3 March, 1969], No. 1186/70. Heading B3D. A method of forming teeth in a workpiece utilizing a tool for successively cutting tooth slots in the workpiece comprises providing a relative infeeding motion between the tool and workpiece so that the tool enters into the workpiece a set predetermined distance for the cutting operation, providing an indexing motion between the workpiece and tool after each tooth slot is cut, measuring the size of a previously cut tooth slot, and varying the predetermined distance of relative infeed between the workpiece and tool for a subsequently cut tooth slot if the previously cut tooth slot is not of a predetermined size. The workpiece may be in the form of a gear or toothed face member such as a coupling or clutch in which face splines are cut and, in apparatus for carrying out the method, the tool is in the form of a cup-shaped grinding wheel. The teeth are cut by a rough grinding, float grinding and finish grinding process and the grinding wheel is periodically dressed so as to have grooves in its cutting surface to permit the flow of coolant to the grinding area. The machine is controlled automatically by an electrical system in conjunction with information stored on a tape. The machine has a rotary work-table 30, Figs. 1 and 3, which is indexable to bring successive teeth of a workpiece clamped thereon beneath the grinding wheel 28 carried by a slide 26 vertically movable in a column 24, the latter being horizontally movable along slideways 32 on a base 22 by a piston-and-cylinder 36, 38 between a retracted position permitting loading and unloading of a workpiece on the table 30 and an advanced, operative position. Fine adjustment of the advanced position may be effected by a motor 40 driving a lead screw and nut. The slide 26 is vertically movable between an upper position and a lower position, for dressing or grinding, by a piston-and-cylinder 42, 44 and fine adjustment of the lower position is provided by a motor 50 driving a lead screw and nut. Dressing of the side surfaces 273, 275, Fig. 11, of the wheel for rough grinding is effected by a pair of rotary dressing wheels 98, 100, and the lower surface 276 of the wheel is dressed by a dressing wheel 101, the three dressing wheels being carried by a bracket 58, Fig. 3, movable about a pivot 60 on the vertical slide 26 by an hydraulic ram 62 between inoperative and operative position. A second dresser 66 having point dressing wheels and movable likewise about a pivot 68 by an hydraulic ram 69 is provided for dressing the wheel for finish grinding. The grinding wheel is connected by a free clutch 74, Fig. 4, to a spindle 72 journalled in a quill 76 supported by bearings 102 in the vertical slide 26. The spindle is connected by a spline 79 permitting relative axial movement to a shaft 78 connected by a belt drive 84 to a motor 80 to effect rotation of the grinding wheel. The upper end of the shaft 78 is connected by a clutch 126 to a gear 128, the clutch being releasable by operation of an hydraulic motor 130. The quill 76 is joined to a screw 94 engaged by a nut 96 rotatable by gearing 108, 110 driven from a motor 112. The gear 128 is connected by gearing 144, 146, Fig. 5, to a multi-lobed cam 150 engaging a follower 152 joined to a core 172 of a displacement transducer 176, the coil 174 of which is mounted in a housing 176 carried by a mount 180 slidable on the quill 76 by a stepping motor 182. Rotation of the cam, through the transducer 176 causes axial reciprocation of the grinding wheel during its rotation while being rough dressed by the dressing wheels 98, 100, 101, so as to form grooves 284, Fig. 12, in its cutting surfaces, which grooves permit the flow of coolant fluid to the grinding area. Indexing of the work-table 30 is effected through a worm wheel 238, Fig. 9, engaged by two worms 240, 242. Worm 240 effects the indexing and is driven by a motor 244 driving an index cam 249, gearing 251 and a clutch 252. A further motor 255 is provided for tramming the workpiece during setting up. A bell crank cover 258 and piston-and-cylinder 260<SP>1</SP>, 262<SP>1</SP> are connected between a bracket 254 carrying worm 240 and a bracket 256 carrying worm 242 to act on the latter to eliminate backlash in the worm 240 and worm gear 238. The bracket 254 of worm 240 is connected to a sine bar 264 slidable in a wedge member 263 movable by a motor 260 controlled from a reader 266. The indexing step effected by the motor 244 driving the worm 240 is always less than actually required since the motor 260 moves the wedge to subtract from the indexing movement and is then operated under the control of the reader 266 to accurately complete the indexing step.  Gauging of the teeth ground in the workpiece during finish grinding is effected by a probe 286, Fig. 14, forming part of a linear velocity displacement transducer 288 carried by wheel housing 26. An air jet is provided adjacent the probe to clean the tooth before it is contacted by the probe. The probe detects any error in a ground tooth and this error is fed through an amplifier to a controller which corrects the face of the grinding wheel for the next tooth to be ground. The machine includes a number of clamps for the slides and workpiece, limit switches, tachogenerators associated with the various motors, and readers for the position of the table and quill, and all these features are controlled by an electro-hydraulic circuit, the electric circuit incorporating various controllers operated under the control of a perforated tape. The rough grinding is initiated from a position in which the workpiece is mounted on the table 30, the housing 26 is fully withdrawn, the quill 76 and table 30 are at zero positions, all parts are clamped, pumps are on and dressers retracted. The tape is read to operate motor 112 to withdraw the quill 76 a predetermined distance and the rotary dresser 58 is advanced, coolant being supplied thereto and the motors rotating the dressing wheels 98, 100, 101 are started. The quill is then advanced to its initial position by motor 112 and then further advanced, say 0À010 inches, to feed the grinding wheel, which at this stage is not rotating into the dressing rollers for a dressing feed. The motor 80 is started to rotate the grinding wheel and, with clutch 126 engaged, the multi-lobed cam 150 is notched, the cam, through the transducer 126, causes axial reciprocation of the grinding wheel so that the grooves 284 are dressed into the wheel. After dressing of the wheel, the clutch 126 is disengaged to render the cam 150 inoperative, the quill is withdrawn by operation of motor 112 and the dresser 58 retracted. Coolant is then supplied to the grinding wheel, the quill advanced at rapid speed and the grinding wheel is rotated at grinding speed. The pressure in cylinder 262<SP>1</SP> of the backlash worm 242 is released to form the table 30 for indexing by motor 244 and worm 240. The quill is then advanced at a predetermined rate through a grinding depth to rough grind a tooth in the workpiece and is then withdrawn the amount of the grinding depth at rapid rate. The workpiece is indexed for rough grinding of the next tooth, the process being repeated until all the teeth have been rough ground whereupon the vertical slide is withdrawn, coolant is transferred from the grinding wheel to the dresser, and the grinding wheel and coolant pump are stopped. The grinding wheel is dressed and the workpiece ground by a "float" grinding operation followed by finish grinding after the rough grinding operation. The dressing for the "float" and finish grinding operations is effected by the point dresser 66. The quill is retracted as before to permit advance of the dresser 66, coolant is supplied to the dresser and the grinding wheel rotated and advanced for a dressing feed, the arms of the dresser then being moved to traverse the points of the dresser across the wheel which during this dressing operation, is not axially reciprocated. After dressing, the dresser is retracted to the quill advanced to its initial position. The quill is then further advanced at a rapid rate to within a few thousandths of hitting the workpiece and then to the "float" grinding position in which no infeed is supplied to the wheel so that all the teeth are ground uniformly and any loose particles on the grinding wheel are removed. During "float" grinding the table is indexed as for rough grinding without precision positioning using the reader 266 and sine bar 264. During finish grinding, the feed of the grinding wheel is first at a rapid rate to within a few thousandths of touching the workpiece and is then fed so as to have a small grinding depth of say, 0À002 inch. The table 30 is indexed, after retraction of the grinding wheel, by the motor 244 and worm 240, the motor 260 moving the wedge 263 of the sine bar 264 so that the amount of indexing movement by worm 240 is less than required. Accurate positioning of the table is then completed under the control of the reader 266 actuating motor 260 to move the wedge 263. After the first indexing operation, the grinding wheel is stopped, an air supply cleans the tooth which has been cut, the coolant supply is cut-off, and the gauge 286 is set. The second tooth is then ground and, after indexing and with the grinding wheel above the third tooth, the gauge is inserted to measure the second tooth. If any error is detected by the gauge, the feed of the grinding wheel is corrected so that the third tooth is ground to size. If, however, this tooth is not ground to size, any error is detected by the gauge before grinding of the next tooth. The process is repeated until all the teeth have been finish ground.